In a case where oil leaked to a pit, a drain, or the like in a factory has flowed out to a river, the sea, or the like, or oil has flowed out to a river, the sea, or the like due to illegal dumping, an accident, or the like, and the like, an oil film floats on a water surface thereof. Such an oil film floating on the water surface is required to be quickly and consistently recovered.
The absence of complete recovery of the oil film leaked to a river, the sea, or the like causes such environmental pollution as has a serious adverse effect on fishes, algae, and the other underwater creatures. Further, the absence of quick recovery causes the oil film to adhere to stones, wall surfaces, or the like of a riverbank or seashore, resulting in making the recovery difficult.
Therefore, conventionally, there have been proposed various recovery apparatuses and recovery methods for such an oil film. As the mainstream thereof, there has been employed a system in which a submersible pump or a suction pump (pump to suck water) draws the oil film below a water surface and sucks up it.
In this system, by disposing a suction port of a suction hose in a position close to the water surface in the water, and sucking by using the submersible pump or the suction pump, the oil film is sucked together with surface water. The sucked oil-water mixed solution is stored in an oil-water separation tank and separated into oil and water by various oil-water separation devices of a cyclone system, a corrugation system, and the like, and the water is drained as it is, and the oil is recovered and reused.
However, in such a conventional recovery system of an oil film, while sucking a large amount of water, the oil film on a water surface thereof is recovered, so that a ratio of oil in the recovered oil-water mixed solution has been very small to be generally 0.1% or less. Therefore, there have been problems that very long time is required for the recovery of the oil film and, a huge oil-water separation tank is needed and long treatment time of oil-water separation is also required, and the like.
Further, when the oil film on the water surface is sucked together with the large amount of water, the oil film becomes fine drops and disperses in the water, so that it has been very difficult to recover all of them.
In order to solve such problems, the present inventor has proposed, in advance, an oil film recovery method and an oil film recovery apparatus for not performing the recovery of the oil film floating on the water surface from the water, but sucking and recovering it from above the water surface, as described in Patent Literature 1.
These have been the ones intended to make a suction port of a tip portion of a suction hose downward face an upper portion at a height of 5 to 200 mm from the water surface, and to suck and recover the oil film together with air and water from the suction port of the suction hose by using a suction mechanism of the suction pump or the like.
Further, for example, Patent Literature 2 also discloses a spilled oil recovery apparatus in which a suction port of a suction pipe of an oil suction device is disposed above the water surface, and oil floated on the water surface is sucked and recovered from above the water surface.